Controlled composition welding method

ABSTRACT

This invention relates to a method and apparatus for controlling the composition of a weld. More particularly it relates to welding using an electric circuit, thereby creating a weld puddle, and adding at least one filler that is electrically independent from the electric circuit to the weld puddle at a controllable rate to obtain a target weld composition. The filler can be added to the extent limited by practical weld puddle geometry and, thus, the method and apparatus also facilitate increased weld deposition rates.

BACKGROUND OF THE INVENTION

[0001] b 1. Field of the Invention

[0002] The invention relates to a method for welding. More specifically,the invention is concerned with a method for welding that provides forincreased control of the weld composition and an increased welddeposition rate.

[0003] 2. Description of the Related Art

[0004] Welding is often not an ideal method of manufacture or repair.Achieving weld metal deposits to satisfy composition, materialproperties and production requirements cannot always be accomplishedwith readily available or off-the-shelf welding consumables. Specialmelts or lots of bare wire, rod, or fluxes can be obtained, but notwithout any combination of impediments, such as observing minimumquantities, extended lead times, and premium prices. Due tomanufacturing restrictions certain chemical composition or mechanicalrequirements cannot even be achieved with special consumables. Desiresto increase production deposition rates are commonly thwarted by complexcomponent geometry and the limitations of the available shop equipmentand power, including the chosen welding process.

[0005] Two particular welding methods show opportunity for improvement.The submerged arc (SAW) and electroslag (ESW) welding processes havebeen used for several decades to deposit high quality corrosionresistant or hardfacing deposits using the strip clad technique in avariety of industries. In the power industry, SAW and ESW have seenextensive use in the cladding of reactor pressure vessels, piping, andlarge bowl, or coal mill rolls where corrosion or wear present problems.ESW and SAW are also used in surfacing techniques where the objective isto deposit additional material to counteract or anticipate the effectsof erosion or abrasion. The difference between surfacing and claddingtechniques resides more in the desired material composition and functionthan the method used to apply the material.

[0006] These processes and other traditional arc-welding processessuffer from limitations associated with the ability to control (or vary)deposit composition. Thus, the composition of the weld is approximatelyconstant over the surface of the product, even though different surfacematerial properties and, therefore, a different weld deposit compositionare desired. Composition has also traditionally been restricted tocommercially available wrought wire and strip alloys, and productionfluxes. The manufacture of tailored consumable compositions is oftenexpensive since the manufacturer must melt an entire heat (or load) ofmaterial to use the processing equipment efficiently. Such heats canrange in size from 2000-20,000 lbs. Since a typical consumable costsapproximately $8.00 per pound one can easily see that it becomestremendously expensive to develop “tailored compositions.”SAW, ESW, andtraditional arc-welding methods are also limited in their abilities tovary the quantity of the weld deposited. Arbitrary variation in the welddeposit is difficult because typical consumable electrodes present arcmaintenance problems (or the ESW equivalent) related to the powersupplied, feed rate, feed angles, electrode extension, and arc length.The feed angle is that angle between the consumable electrode and thewelded piece. The arc length is the distance between the two. Theseissues combine to make variation in the feed rate a non-trivial changein the welding process.

[0007] Should two such electrodes be used to make one deposit, the arcsof such electrodes also become unstable if fed at different rates. Theadditional angles and gaps between the second consumable electrode andboth the first consumable electrode and the welded piece must becontrolled. This further limits the potential weld composition variationand makes any variation at all more difficult. The electrode material isfinally limited to materials that conduct electricity in the mannernecessary to establish an arc and melt at a desired rate.

[0008] The combination of two consumable electrodes also presents thefurther problem of “arc blow.” Arc blow is an undesired phenomena inwhich a weld deposit splatters instead of flowing to the intendedlocation. Arc blow can occur because flowing current creates a magneticfield. With two electrodes the magnetic field from one can repulse theother resulting in force on the flowing melted weld metal to the pointit splatters and potentially extinguishes the arc.

[0009] In general, where weld deposit consumables are current carryingelectrodes, any variation in the feed rate of a single electrode affectsthe power to the weld puddle and, thus, the overall weld processincluding heat input, weld puddle geometry, weld composition, anddeposition rate. There is, therefore, a need in the industry for abetter welding method to easily and economically vary composition,improve weld deposition rates, provide better control of heat input, andweld puddle geometry.

BRIEF SUMMARY OF THE INVENTION

[0010] This invention provides a method for welding. A first embodimentof the method comprises welding a workpiece using an electric circuit,thereby creating a weld puddle, and adding at least one filler that iselectrically independent from the electric circuit to the weld puddle ata controllable rate to obtain a target weld composition. A secondembodiment comprises causing electric current to flow among a primaryelectrode, a flux, and a workpiece to be welded, thereby creating a weldpuddle, passing the electric current through the weld puddle to createresistance heating; and adding at least one filler that is electricallyindependent from the electric circuit to the weld puddle at acontrollable rate to obtain a target weld composition. A thirdembodiment comprises causing an arc between a primary electrode and aworkpiece to be welded, thereby creating a weld puddle, maintaining thepuddle with heat created by the arc, the arc being located within theweld puddle, and adding at least one filler that is electricallyindependent from the electric circuit to the weld puddle at acontrollable rate to obtain a target weld composition. In addition thesethree methods can be used to obtain an increased weld deposition rate.

[0011] The invention also provides an apparatus for controlling thecomposition of a weld. A first embodiment comprises means for creating aweld puddle on a workpiece, and means for introducing at least oneadditional filler, that is independent from the means for creating theweld puddle, into the weld puddle at a controllable rate. A second suchembodiment comprises a first consumable electrode, a second electrode, apower supply; an electric circuit established by connecting the secondelectrode to the power supply and the workpiece, by connecting the firstelectrode to the power supply, and by establishing current flow betweenthe first electrode and the workpiece, and at least one fillercontroller that is independent from the electric circuit and wherein thefiller controller controls the rate at which at least one fillermaterial is added.

[0012] The ability to tailor the composition of a weld provides benefitsin the application of consumable alloys which are inherently difficultto fabricate. Solid welding consumables (wire or strip) are difficult tomanufacture or fabricate in certain applications due to expense ortechnological limitations of drawing the consumable to a small diameter.The use of tailored compositions will help overcome this obstacle.Essentially, the present invention provides the ability to cast adesired consumable composition “in place.” Such an ability allows a weldcomposition to be tailored so that the material properties, such ascorrosion resistance, hardness, or strength, of the weld are more suitedfor the designed function of a particular location on the workpiece.Adding filler directly to the weld puddle also increases the depositionrate of the weld process without complicating the maintenance of the arcor other weld puddle-forming procedures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0013]FIG. 1 illustrates a preferred embodiment of the invention using asubmerged arc welder;

[0014]FIG. 2 illustrates a further preferred embodiment of the inventionusing an electroslag welder;

[0015]FIG. 3 illustrates an additional preferred embodiment of theinvention using an arc welder;

[0016]FIG. 4a contains a flowchart of a preferred embodiment of themethod of the invention; and

[0017]FIG. 4b contains the continuation of the flowchart of FIG. 4a.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The foregoing and other aspects and advantages will be betterunderstood from the following detailed description of the preferredembodiments of the invention with reference to the drawings. Likereference numerals refer to corresponding parts throughout the drawings.

[0019] The present invention provides an improved method of weldingwhereby the composition of a weld, and thus the component or workpiece,can be tailored during welding to meet specific material requirements ofthe component at specific locations on the component. Among theserequirements are the mechanical properties, such as strength andtoughness, and corrosion resistance.

[0020] Referring now to FIG. 1, which illustrates a preferred embodimentof the invention using a submerged arc welder (SAW), SAW 10 is generallycomposed of power source 12, control panel 14, electrode lead 16, worklead 18, consumable electrode 20, machine consumable electrode feeder22, and flux feeder 24. SAW 10 operates on workpieces 25, 26 to formweld 28 underneath solid slag 30. SAW 10 is shown joining workpieces 25,26, but one of skill in the art will recognize that the invention,described with respect to the joining operation, could also beimplemented using SAW 10 to clad or surface a workpiece, or build up aweld, such as weld 28. SAW 10 begins operation at tab 32 with theinitiation of an arc (not shown) between consumable electrode 20 andworkpieces 25, 26 in welding vee 38, although tab 32 is not alwayspresent, particularly on circumferential weldments. Flux 34 is thenadded via flux feeder 24 to the surface of workpieces 25, 26 therebycovering the arc, although, for purposes of illustration, FIG. 1 doesnot show flux 34 covering weld puddle 36. Welding vee 38 is formed bybeveling the edges of workpieces 25, 26. Weld puddle 36 is formed inwelding vee 38 by melting consumable electrode 20, flux 34, andworkpieces 25, 26. After weld puddle 36 forms, filler 40 is added toweld puddle 36 with the rate of filler feeder 42 determined to give weld38 a desired composition.

[0021] The composition of filler 40 is chosen depending primarily uponthe desired final composition of weld 28. Other factors that arebalanced in making the choice include: the compositions of flux 34,workpieces 25, 26, consumable electrode 20, and the rate of travel ofconsumable electrode 20 along welding vee 38 in direction 44. Filler 40is added directly to weld puddle 36. Filler 40 may be added at aconstant rate for the length of weld 28. Filler feeder 42 may also becontrolled to vary the rate at which filler 40 is added to vary thecomposition of weld 28. Since filler 40 is not an electrode and is addeddirectly to weld puddle 36, the rate it is added may vary over a widerange. This range is bounded on the low side by zero filler and on thehigh side by the practical shape of the weld puddle. Excessive fillercould cause the weld puddle to run, or solidify too quickly due to heattransfer to filler material, among other effects known to one of skillin the art. But one desirable effect of using extra filler to cool weldpuddle 36 is that the cooled weld puddle has increased surface tensionand, thus, weld puddle 36 can be larger due to the extra surface tensionof holding cooled weld puddle 36 together. This is particularly usefulon a rounded surface, which increases the forces tending to disperseweld puddle 36. The larger weld puddle results in an increaseddeposition rate.

[0022] Filler 40 also need not be the only additional filler added toweld puddle 36. A second additional filler (see FIG. 3, element 44)could be added to weld puddle 36 simultaneously with filler 40, orinstead of filler 40, depending upon the desired composition of weld 28.In fact, any number of additional fillers could be added to weld puddle36 so long as the total additional filler added does not exceed thelimit set by the practical weld puddle shape or thermodynamicconsiderations known to one of skill in the art. Similarly, the rate atwhich consumable electrode 20 is added may also be varied providing thatweld puddle 36 retains the properties necessary to create the desiredweld 28.

[0023] In general, effective energy input to workpieces 25, 26 and weldpuddle 36 is a function of the consumable electrode parameters, allfiller parameters, and the speed at which the weld apparatus travelsover the workpiece surface. In particular, with respect to FIG. 1, aswell as FIGS. 2 and 3, consumable electrode 20 is preferably introducedperpendicularly to workpieces 25, 26, or within ten degrees ofperpendicular. Lesser angles of introduction increase the risk thatconsumable electrode 20 will lose contact with weld puddle 36, causingweld penetration to suffer. Correspondingly, filler 40 and filler 44(FIG. 3) are preferably introduced into weld puddle 36 at angles lessthan 60 degrees from workpieces 25, 26. Here, greater angles increasethe risk that fillers 40, 44 will stub out prior to melting.

[0024] Referring now to FIG. 2, we see a further preferred embodiment ofthe invention using an electroslag welder (ESW). ESW 11 works to formweld 28 under molten slag bath to join vertical workpieces 25, 26. ESW11 is shown joining workpieces 25, 26, but one of skill in the art willrecognize that the invention, described with respect to the joiningoperation, could also be implemented using ESW 11 to clad or surfaceworkpiece 26, or build up a weld, such as weld 28, if the workpiece andnecessary apparatus, such as retaining shoes 48 were properly oriented.ESW 11 initiates the joining of workpieces 25, 26 by initiating an arc(not shown) between consumable electrode 20 and workpieces 25, 26 at aninitial location. This arc creates heat that melts consumable electrode20 in addition to portions of workpieces 25, 26 and forms weld puddle36. If consumable electrode 20 is flux-cored its melting provides fluxto form molten slag bath 35, otherwise flux must be added to theprocess. With the formation of weld puddle 36 and molten slag bath 35the arc is extinguished, and the passage of electrical current fromconsumable electrode 20 through the resistance of molten slag bath 35and weld puddle 36 provides the resistance heating necessary to sustainweld puddle 36. At this point filler 40 can be added through molten slagbath 35 into weld puddle 36. As with SAW 10 of FIG. 1, filler 40 ischosen depending upon the desired composition of weld 28. As weld 28progresses up workpieces 25, 26 retaining shoes 48, which are watercooled, are repositioned to retain molten slag bath 35 and weld puddle36 between workpieces 25, 26, although retaining shoes 48 are not shownin total in FIG. 2 for illustrative purposes. Should it be necessarybecause of the thickness of workpieces 25, 26, both consumable electrode20 and filler 40 could be horizontally oscillated by consumableelectrode feeder 22 and filler feeder 42 in direction 45. Also as withSAW 10 of FIG. 1, and as illustrated in FIG. 3, additional fillers couldbe added to weld puddle 36 in addition to filler 40 for the purpose ofvarying the composition of weld 28.

[0025] Referring now to FIG. 3, we see illustrated an additionalpreferred embodiment of the present invention using a typical arc-welder13. Here, arc-welder 13 is surfacing or cladding workpiece 26, by layingdown layer 27. Layer 27 is initiated with the formation of arc 37between consumable electrode 20 and workpiece 26. The heat from arc 37forms weld puddle 36 by melting workpiece 26 and consumable electrode20. Upon formation of weld puddle 36 additional fillers 40 and 44 may beadded to weld puddle 36 to form layer 27 with a desired composition.After consumable electrode 20 and additional fillers 40 and 44 arepassed over workpiece 26, or arc welder 13 is moved in horizontaldirection 45, workpiece 26 is moved in direction 44 for anotherhorizontal pass.

[0026] Arc-welder 13 may only use a single additional filler, or mayvary the feed rates of additional fillers 40 and 44 to form a layer ofvarying composition, just as ESW 11 and SAW 10 could use a single filleror multiple fillers. Such compositional variation could be needed due tothe need for different locations on the workpiece to have differentmaterial properties such as, for example, corrosion resistance,strength, or hardness. A second layer 29 serves to illustrate how thecomposition of the weld deposited could be varied in three dimensions byvarying consumable electrode 20 plus fillers 40 and 44. Where layer 27is an inner layer and the material property needed might be toughness,or strength, additional fillers 40 and 44 would be chosen to impartthose material properties. But if layer 29 is then an external layer andmore corrosion resistance is required, then additional fillers 40 and 44could be varied in their deposition rate, or composition so that layer29 achieves the desired corrosion resistance. In this manner a workpiececould be surfaced with many layers, with the inner layers possessing thestrength and toughness necessary for the loads the workpiece is to bear,and the outer layer possessing improved corrosion resistance forimproved overall longevity. In fact, each layer in a multi-layeredcladding could be made a different composition just by varying thefillers used.

[0027] The preferred embodiment of the invention as depicted in FIG. 3could be used in weld buildup of turbine discs where excellent corrosionresistance is desired at the blade attachment region, yet high strengthis also necessary. Most of the weld would be with a high tensile, highyield strength filler that matched the inner blade metal, with a gradualchange in filler composition to a corrosion resistant filler over thelast few layers. This would assure excellent weld properties. Also, bothSAW 10 (FIG. 1) and ESW 11 (FIG. 2, modified for a horizontal workpiece)welding apparatuses could be used to clad or surface weldpiece 26 inFIG. 3, in addition to arc welder 13.

[0028] Similarly, in applications requiring high wear resistance (suchas valve seats, steel mill rolls, or other material handling/crushingequipment), the weld composition could be tailored over the final fouror so layers to go from an alloy steel base metal with poor wearresistance to a hardfacing alloy at the surface with very high wearresistance by selecting the appropriate consumable electrode, fillersand rates of addition. Since many hardfacing consumables are difficultto apply due to the dissimilarity between the base metal substrate andthe hardfacing material, this use of tailored compositions wouldminimize this difficulty by allowing the change from alloy steel tohardfacing steel to be gradual, thus minimizing the dissimilaritybetween any two layers.

[0029] The invention would also benefit gears. Typically, gears arecarburized to develop good wear resistance at the surface whilemaintaining high toughness and strength throughout the remainder of thegear. The use of tailored compositions would allow the engineer tofabricate high wear resistant gears via welding, thus eliminatingpotential concerns over decarburization of the surface wear region.

[0030] Now referring to FIGS. 4a and 4 b, we describe a flowchart of apreferred embodiment of the method of the invention. Step 50 is todetermine the target weld compositions for specific locations on aworkpiece or component. As discussed with respect to FIGS. 1, 2, and 3,the target compositions can vary according to location on the workpiece,depending upon the material properties desired for that location, and inthree dimensions. Step 52 is to choose the filler or fillers necessaryfor the weld to achieve the target compositions of step 50. One of skillin the art will know to select fillers from those commercially availableor fabricated fillers that contain the elements and materials needed toachieve the target composition, if the selected fillers are added in theappropriate amounts. Thus, the desired total weld deposition rate mustalso be considered in this step. Step 54 is to set the rate of additionfor each filler for specific locations so that the combined fillers andweld puddle leave a weld of the desired target compositions at thoselocations, again also considering the desired total weld depositionrate. Step 56 is to weld the workpiece to create a weld puddle. Asillustrated in FIGS. 1, 2 and 3, there are many ways to create a weldpuddle that are suitable. One of skill in the art will recognize thatmany ways exist for creating the heat necessary to form a weld puddleand practice the current invention, in addition to those illustrated inthe preceding Figures. Step 58 is then to add the necessary fillers tothe weld puddle at the rates determined to yield the target weldcomposition. Step 60 is to move to a new location on the object afterthe weld of step 58 is completed. That “new” location could in actualitybe the same location if more weld deposit is desired at that spot or ifa different weld composition is desired over the previous weld. Itshould be noted that the present method is described in discrete steps,reflecting discrete movements for simplicity, but in actual practice themovement from weld location to weld location would be continuous, andthe weld fillers used and the rates at which they would be added wouldalso be adjusted continuously, or as necessary. In this way, step 56need only be performed at the beginning of the weld, since the propercontinuation of the weld process works to perpetuate the weld puddle.Step 62 is to determine whether, at the new location of step 60, a newweld composition is desired. If so, then the method is to proceed tostep 64 of FIG. 4b. If not, then steps 58 through 60 are simply repeateduntil the entire weld is complete (and the answer to step 74 is todiscontinue welding).

[0031] If a new target weld composition is desired, then step 64, nowreferring to FIG. 4b, is to determine whether the new target requires achange of fillers, and step 66 is to change the filler if necessary. Theactual change of filler could be accomplished by numerous means, such asstopping one filler feeder and starting another, in addition to simplyreloading a filler feeder with a different filler. Step 68 is todetermine whether the new target composition requires any additionalfillers. Should that be necessary, step 70 is to introduce the necessaryfillers. It should be apparent to one of skill in the art that thechoice of fillers is so dependent upon many factors including cost andavailability that one desired weld composition could be achieved usingany number of fillers and feed rates, depending upon the fillers chosen.

[0032] Step 72 is then to set the rate of addition of each chosen fillerso that when added to the weld puddle, the combined fillers and weldpuddle leave a weld of the desired composition. After step 72 the methodreturns to step 58 and follows the method until step 74 directs you toend welding.

[0033] The above Figures have described areas where compositionalcontrol of weld 28 is important. A second and similarly important aspectof the invention is the ability to increase the deposition rate overthat of currently used processes due to the increased ability to addmultiple fillers at varied rates independently from the creation andsustaining of weld puddle 36. Excess (or unused) energy is normallyassociated with the processes depicted in FIGS. 1, 2, and 3 and this isnormally dispersed into previous weld layers or the base metalsubstrate. The introduction of a secondary filler makes use of thisexcess energy and thereby increases the total weld deposit.

[0034] Two applications where the technology would be useful include theweld buildup of turbine rotors or discs and heavy equipment welding,such as earthmoving equipment. Weld buildup on rotors or discs wouldenable utilities to dramatically decrease the amount of time it takes torepair a turbine via welding. Weld buildup on heavy equipment, inaddition to decreasing repair time, would benefit from the invention'sability to achieve weld buildups with wear resistant compositions toincrease the longevity of equipment such as bulldozer blades, blades onpans, dredging equipment, or drag lines.

[0035] With the welding method described herein a desired compositioncan be developed through welding. Significant savings can be realized,as some specialized solid welding wires can run over $100 per lb, sincethe purchase of small or large batches of such special materials areunnecessary where the method of the present invention allows thecreation of the same composition through multiple fillers. Furthermore,multiple weld compositions can be generated and optimized for thedesired component service conditions.

[0036] Finally, this invention can be utilized for the manufacture,fabrication, repair or modification of: steam or industrial turbinerotor/disc components, bowl mills and rolls, waterwall cladding andtubes, fan components, nuclear waste/transportation casks, vessel andpipe interior and exterior cladding. Further uses include: blowoutpreventers, valves, steel mill components, concast rolls and ladlerefurbishment, rail build-up and repair, heavy equipment related tomining and material handling such as crushers and conveyors, marinepropeller shafts and sea chests. Additional other uses are: centrifugalcasting molds, die repair, plate overlay in lieu of explosion or otherbonding methods. Any commercial application which involves manufacture,fabrication, or repair of heavy industrial components will benefit fromthis technology due to its ability to control composition, metallurgicalstructure, shrinkage, distortion, and residual stress.

EXAMPLE 1

[0037] The following example describes the creation of a tailored weldcomposition in an exemplary embodiment according to the presentinvention. This example shows the method of the invention used to changethe composition of a weld, with the weld created using a submerged arcwelding technique and apparatus such as that illustrated in FIG. 1.Also, this example uses multiple filler wires, as depicted in FIG. 3,fillers 40 and 44, to change both weld composition and weld depositionrate. For the purposes of this example, only the Cr and Ni content andtheir changes will be discussed. It is important to note that the secondfiller (wire) used is considerably higher in Cr and lower in Ni than the150003-1 strip filler. (See Table 1 for filler compositions.)

[0038] Now referring Table 2, we see that for a weld made with the stripfiller 150003-1, and no secondary filler (Test Bead # P2B14), the Cr andNi content are 0.28 and 2.45 wt. % respectively. (See Table 3.) If asingle wire is added (Test Bead # P2B15) the composition changes to 1.25wt. % Cr and 2.20 wt. % Ni. Adding a second wire (Test Bead # P3B3)provides a new composition of 2.18 wt. % Cr and 2.01 wt. % Ni. Allwelding parameters were held constant for the three welds with theexception of the secondary wire addition.

[0039] The weld composition changes radically from one test to the next.The beginning Cr content changed from 0.28 to 2.18 wt. %. Additionally,the Ni content was lowered from 2.45 to 2.01 wt. %. The method creatednew weld compositions depending upon the amount of wire added andrealized a greater amount of wire deposited. This particular examplealtered the number of wires and wire feed rate, but a similar resultcould be had by changing only the wire feed rate. TABLE 1 Chemicalcomposition of the strip filler material 15003-1 and the 1.6 mm diametermetal core wire filler material, M91. C Mn Si Cr Ni Mo Strip 150003-10.12 1.7 0.15 0.33 2.6 0.6 Wire 0.08 0.96 0.32 8 0.26 0.96

[0040] TABLE 2 Four layer test deposits demonstrating the ability toincrease the weld deposition rate by adding additional filler. Note theincrease in deposition rate (lbs/hr) by introducing one, then twosecondary filler materials. # Strip Deposition Strip Lay- Feed,Additional Rate, Test Filler Flux ers ipm wire feed, lbs/hr. P2B14150003-1 SA120 4 72 None 26.39 P2B15 150003-1 SA120 4 72 1 @ 66 ipm29.30 P3B3 150003-1 SA120 4 72 2 @ 66 ipm 32.20 P3B5 150003-1 SA120 4 852 @ 100 39.97 ipm P3B10 150003-1 SA120 4 85 2 @ 125 42.17 ipm

[0041] TABLE 3 Resulting weld chemistries of four layer test depositsdescribed in Table 2. Note the ability to alter composition of thechromium and nickel levels by the introduction of a secondary wire(s).Test Bead Number C Mn Si Cr Ni Mo P2B14 0.086 1.49 0.51 0.28 2.45 0.58P2B15 0.086 1.46 0.51 1.25 2.20 0.65 P3B3  0.094 1.35 0.44 2.18 2.010.71 P3B5  0.092 1.40 0.47 2.19 2.00 0.70 P3B10 0.089 1.34 0.44 2.571.91 0.72

[0042] It is to be understood that while illustrative embodiments of theinvention have been shown and described herein, various changes andadaptions in accordance with the teachings of the invention will beapparent to those of skill in the art. Such changes and adaptionsnevertheless are included within the spirit and scope of the inventionas defined in the following claims.

We claim:
 1. A method for welding, comprising: welding a workpiece usingan electric circuit, thereby creating a weld puddle; and adding at leastone filler that is electrically independent from said electric circuitto said weld puddle at a controllable rate to obtain a target weldcomposition.
 2. The method of claim 1, further comprising varying saidcontrollable rate during said welding.
 3. The method of claim 1, whereinsaid adding is performed at a controllable rate for each said at leastone filler.
 4. The method of claim 3, further comprising varying saidcontrollable rate for at least one of said at least one filler duringsaid welding.
 5. The method of claim 1, wherein said welding comprisestraversing a weld region and said adding comprises: adding said at leastone filler at a first location within said weld region; and adding atleast one additional filler material that is electrically independentfrom said electric circuit to said weld puddle at a second locationwithin said weld region at a second controllable rate to obtain a secondtarget weld composition.
 6. The method of claim 5, further comprisingvarying said second controllable rate during said welding.
 7. The methodof claim 5, wherein said adding at least one additional filler isperformed at a controllable rate for each said at least one additionalfiller.
 8. The method of claim 7, further comprising varying saidcontrollable rate for at least one of said at least one additionalfiller during said welding.
 9. The method of claim 1, wherein saidwelding uses a submerged arc.
 10. The method of claim 1, wherein saidwelding uses electric current to create resistance heating.
 11. Themethod of claim 1, wherein said adding comprises adding said at leastone filler selected from the group consisting of: a filler having acomposition comprising a wrought material; a filler having a compositioncomprising a sintered material; a filler having a composition comprisinga flux; a filler having a composition comprising a metal cored material;and a filler having a composition comprising a composite material. 12.The method of claim 1, wherein said welding comprises surfacing saidworkpiece.
 13. The method of claim 1, wherein said welding comprisesjoining a second workpiece to said workpiece.
 14. The method of claim 1,wherein said welding comprises building up a weld on said workpiece. 15.The method of claim 1, wherein: said welding comprises welding aparticular location on said workpiece having a particular metallurgy;and said target weld composition is compatible with said particularmetallurgy.
 16. The method of claim 1, wherein said welding compriseswelding with a consumable electrode added at a primary controllable rateand further comprises varying said primary controllable rate during saidwelding.
 17. The method of claim 1, wherein said adding comprises addingat least one filler that is electrically independent from said electriccircuit to said weld puddle to obtain an increased weld deposition rate.18. A method for welding, comprising: causing electric current to flowamong a primary electrode, a flux, and a workpiece to be welded, therebycreating a weld puddle; passing said electric current through said weldpuddle to create resistance heating; and adding at least one filler thatis electrically independent from said electric circuit to said weldpuddle at a controllable rate to obtain a target weld composition. 19.The method of claim 18, further comprising varying said controllablerate during said welding.
 20. The method of claim 18, wherein saidadding is performed at a controllable rate for each said at least onefiller.
 21. The method of claim 20, further comprising varying saidcontrollable rate for at least one of said at least one filler duringsaid welding.
 22. The method of claim 18, wherein said causing electriccurrent to flow comprises adding said primary electrode at a primarycontrollable rate and further comprises varying said primarycontrollable rate during said causing electric current to flow.
 23. Themethod of claim 18, wherein said adding comprises adding at least onefiller that is electrically independent from said electric circuit tosaid weld puddle to obtain an increased weld deposition rate.
 24. Amethod for controlling the composition of a weld, comprising: causing anarc between a primary electrode and a workpiece to be welded, therebycreating a weld puddle; maintaining said puddle with heat created bysaid arc; and adding at least one filler that is electricallyindependent from said electric circuit to said weld puddle at acontrollable rate to obtain a target weld composition.
 25. The method ofclaim 24, further comprising varying said controllable rate during saidwelding.
 26. The method of claim 24, wherein said adding is performed ata controllable rate for each said at least one filler.
 27. The method ofclaim 26, further comprising varying said controllable rate for at leastone of said at least one filler during said welding.
 28. The method ofclaim 24, wherein said causing an arc comprises adding said primaryelectrode added at a primary controllable rate and further comprisesvarying said primary controllable rate during said causing.
 29. Themethod of claim 24, wherein said adding comprises adding at least onefiller that is electrically independent from said electric circuit tosaid weld puddle to obtain an increased weld deposition rate.
 30. Anapparatus for welding, comprising: means for creating a weld puddle on aworkpiece; and means for introducing at least one additional filler intosaid weld puddle at a controllable rate, wherein said means forintroducing are independent from said means for creating.
 31. Anapparatus for welding a workpiece, comprising: a first consumableelectrode; a second electrode; a power supply; an electric circuitestablished by connecting said second electrode to said power supply andsaid workpiece, by connecting said first electrode to said power supply,and by establishing current flow between said first electrode and saidworkpiece; and at least one filler material that is independent fromsaid electric circuit.
 32. The apparatus of claim 31, further comprisingat least one filler controller wherein said filler controller controlsthe rate at which said at least one filler material is added.
 33. Theapparatus of claim 31, wherein said electric circuit comprises a weldpuddle.
 34. The apparatus of claim 33, wherein said weld puddle usesflux shielding.
 35. The apparatus of claim 33, wherein said weld puddleuses gas shielding.
 36. The apparatus of claim 31, wherein said electriccircuit comprises an electric arc between said first electrode and saidworkpiece.
 37. The apparatus of claim 36, wherein said electric arc islocated within said weld puddle.
 38. The apparatus of claim 32 whereinsaid at least on filler material is added to obtain a target weldcomposition.
 39. The apparatus of claim 32 wherein said at least onefiller material is added to obtain increased weld deposition.